1. Technical Field
The present invention relates to tape storage systems in general. More particularly, the present invention relates to tape storage systems having multi-volume datasets. Still more particularly, the present invention relates to a method and apparatus for handling multi-volume datasets in a tape storage system.
2. Description of Related Art
Virtual tape servers (VTSs) are one of the tape dataset stacking products specifically designed to cater customers demand for an efficient way to manage information stored on magnetic tapes. A VTS system typically includes a host interface, a VTS cache, and an automated library having multiple tape devices.
A VTS system is usually attached to a host computer such as a mainframe computer. When the host computer writes a dataset to the VTS system, the dataset is written to a virtual volume on the VTS system. If a dataset being written to a virtual volume exceeds the capacity of a single virtual volume, the dataset can be written by the host computer to a series of virtual volumes commonly referred to as a multi-volume dataset.
When the host computer reads a virtual volume of a multi-volume dataset from the VTS system, the virtual volume can be retrieved from a VTS cache if the virtual volume is currently resided on the VTS cache. If the virtual volume is not resided on the VTS cache, a storage manager determines which of the magnetic tapes contains the virtual volume. The corresponding magnetic tape is subsequently mounted on one of the tape devices, and the virtual volume is sent from the magnetic tape to the VTS cache and to the host computer. Since tape mounting can be very time-consuming, it is always favorable to have the frequently accessed virtual volumes retained in the VTS cache.
Often, when one virtual volume in a multi-volume dataset is accessed, the other virtual volumes within the same multi-volume dataset will typically be accessed as well. If an application within the host computer is going to access all the virtual volumes in the multi-volume dataset, it would be very advantageous to prestage all the virtual volumes into the VTS cache before they were accessed by the application within the host computer. However, the VTS system generally does not have the knowledge of which virtual volumes belong to a multi-volume dataset; thus, it would be desirable to provide such knowledge to the VTS system.